NEW: Master Swift design patterns with my latest book! >>

How to make custom types from strings using ExpressibleByStringLiteral

Written by Paul Hudson    @twostraws

Swift’s ExpressibleByStringLiteral protocol lets us create any type directly from a string – as long as Swift understands what type you mean, you can create whatever you want.

For example, if you regularly hard-code URLs and are tired of force unwrapping them when you know they are definitely correct, you can make URL conform to ExpressibleByStringLiteral so that URLs can be created directly from strings:

extension URL: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        self = URL(string: value)!
    }
}

With that extension in place you can now write code like this:

let url: URL = "https://www.hackingwithswift.com"
print(url.absoluteString)

Notice that I’ve clearly marked url as being of type URL so that Swift doesn’t think it’s a regular string.

Available from iOS 8.0

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Get my latest video for free

Learn about value types, functional programming, and protocol-oriented programming in this new video – it's free!

Click here to visit the Hacking with Swift store >>